How do I get a level 8 writing a science conclusion?

The best way to practice is to read through conclusions in scientific journals. If you can replicate that, you can get amazing grades!
Generally, in the conclusion, you review your data (if any) and state your opinions and arguments of what the results show in detail. You should quote the data in the results section in support of the scientific conclusion you are making. Such as "as can be seen by graph 5 there is a noticebale difference between group X and group Y which allows the conclusion that ....." etc.
You should state if the hypothesis has been supported or not. Your readers can then decide if they agree or disagree with your conclusions. This is the basis of scientific debate. If the data obtained is not sufficient to support or reject the hypothesis state why and propose further work that will help to generate more data allowing you to be able to draw a firmer conclusion.
Remember, the purpose of a good conclusion is not to prove your point, it's to objectively share your findings based in the data you have available.
Good luck!